1. Technical Field
The present invention relates to circuit board processing and attaching cores. Specifically, the present invention provides a method and structure wherein cores are attached and an electrical connection is made between conductive surfaces on the cores using a metallurgical paste.
2. Background Art
A common procedure in circuit board processing involves laminating multiple cores together. However, generally, the cores are not electrically connected via to via during lamination. For example, one method involves first electrically connecting the cores using conductive pads. After lamination, a hole is drilled through the conductive pads and electroplated with copper to form the via.
An alternative solution uses conductive adhesive to electrically attach vias during lamination. The conductive adhesive is placed onto a via and electrically connects the vias when the cores are laminated together. However, conductive adhesives contain plate-like structures greater than 0.5 mils in size. These plates tend to clog at the top of the holes. Therefore, the adhesives cannot be used effectively with thicker cores and smaller vias. Additionally, conductive adhesives require precious metal for good connections, making the products more expensive. Finally, a substantial number of manufacturing sites are not equipped to handle conductive adhesives. Consequently, significant costs may be required to modify current manufacturing sites to use conductive adhesives.
As a result, there exists a need for a structure and method of attaching cores having vias with conductive surfaces using a conductive material having smaller particle sizes than what is currently used.
The invention provides a method and structure of attaching a plurality of cores.
A first aspect of the invention is directed to a method of attaching a first core to a second core, wherein the first core includes a via having a first conductive surface and wherein the second core includes a second conductive surface, the method comprising the steps of: applying a metallurgical paste onto the first conductive surface, the metallurgical paste including flux; removing a portion of the flux from the metallurgical paste; providing an adhesive sheet having an opening that substantially conforms to the first conductive surface and the second conductive surface; interposing the adhesive sheet between the first core and the second core such that the metallurgical paste on the first conductive surface aligns and contacts the second conductive surface; and joining the first core and the second core.
A second aspect of the invention is directed to a method of attaching a first core to a second core, wherein the first core includes a pad having a first conductive surface and wherein the second core includes a via having a second conductive surface, the method comprising the steps of: applying a metallurgical paste onto the first conductive surface, the metallurgical paste including flux; removing a portion of the flux from the metallurgical paste; providing an adhesive sheet having an opening that substantially conforms to the first conductive surface and the second conductive surface; interposing the adhesive sheet between the first core and the second core such that the metallurgical paste on the first conductive surface aligns and contacts the second conductive surface; and joining the first core and the second core.
A third aspect of the invention is directed to a structure comprising: a plurality of cores attached with an adhesive; wherein at least one core has a via having a first conductive surface; and wherein a metallurgical paste forms an electrical connection between the first conductive surface and a second conductive surface of another core.
The exemplary aspects of the present invention are designed to solve the problems herein described and other problems not discussed, which are discoverable by a skilled artisan.